The present invention relates to a method and system for use in a magnetic disk storage device or a disk array system having plural magnetic disk storage devices for improving their reliability. More particularly, the present invention relates to a method and system for use in a magnetic disk storage device or disk array system for controlling the relationship between the stopping time of a magnetic disk storage device and the interval of operation time of the magnetic disk storage device so as to improve its reliability.
A disk array system known as a RAID (Redundant Array of Inexpensive Disks) system is becoming popular owing to its low price and high reliability and the fact that a disk array system can be easily recovered, even if one of the magnetic disk storage devices included in the disk array system is halted due to some difficulty.
A data recovery method is, for example, disclosed in unexamined Japanese patent publication 6-230903. Namely, when one of the magnetic disk storage devices in the disk array system has failed, correct data is recovered using the data and parity data in the other healthy magnetic disk storage devices. The recovered data is stored in open areas in the healthy magnetic disk storage devices, if the total capacity in the open areas in the healthy magnetic disk storage devices is greater than the amount of data stored in the failed magnetic disk storage device.
However, when plural magnetic disk storage devices have failed at the same time, no particularly effective recovering method other than transferring data from a backup system is available. Thus, such a recovery is beyond conventional methods. Therefore, the occurrence of a failure in plural magnetic disk storage devices at the same time may result in a severe loss of data.
Recording and retrieving data in a magnetic disk storage device is performed by a magnetic head disposed adjacent to a rotating magnetic disk in a head floating space. As magnetic disk storage devices improve the head floating space is decreased because data recording density on the magnetic disk is nearly inversely proportional to the head floating space. In order to obtain a smaller head floating space, the Contact Start Stop (CSS) system is used. The CSS system is a system in which the magnetic head contacts the magnetic disk surface by a pressing force governed by the magnetic head suspension apparatus when the magnetic disk has stopped, and floats at a desired space above the magnetic disk surface when the rotating speed of the magnetic disk has reached a predetermined speed. The magnetic head floats above the surface of the magnetic disk due to a floating force induced by an air-flow on the magnetic disk surface as the magnetic disk rotates. The floating force is balanced by the pressing force generated by the magnetic head suspension apparatus. CSS systems are commonly utilized in conventional magnetic disk storage devices.
In CSS systems, consideration should be given to the tendency over time for the magnetic heads to stick to the magnetic disk surfaces, thereby causing problems during start-up of magnetic disk rotation. Sticking occurs due to the build-up of materials such as contaminants and lubricants in the gap between the magnetic head and the magnetic disc during long term operation of the magnetic disk storage device. Severe sticking between the magnetic head and the magnetic disk is caused by surface tension or sticking force of the contaminants and lubricants when the magnetic head contacts the magnetic disk at the time the rotation of the magnetic disk has been halted. Thus, there are technical problems to be solved in CSS systems in which starting-up problems due to the above-described sticking problem might occur during restart when the magnetic disk storage device has been halted after long term continuous operation. There are no techniques in the conventional technology for addressing this problem.
Therefore, there is great concern to avoid causing simultaneous starting-up problems in plural magnetic disk storage devices of a disk array when the magnetic disk storage devices are stopped after long term continuous operation. Simultaneous starting-up problems in the magnetic disk storage devices of a disk array could cause fatal damage to the magnetic disk storage devices thereby making data recovery impossible. Such fatal damage could be even worse in a data security system where data is recovered only by generating redundant data such as parity data.